I have several different processes within a single project that I work on. I am constantly opening and closing tabs(java files) in the code editor for that particular process.
In addition to all mentioned... Did you try Bookmarks? You can save multiple bookmarks into one set, there are bookmark sets management option and you can add descriptions with prefixes to group bookmarks on the same set. Finally and more important: you can select multiple bookmarks, select goto and multiple editors will be opened at once.